Sound diaphragm



June 16, 1931. E. s. PRIDHAM SOUND DIAPHRAGM Filed May 15, 1929 /3 I VENTOR. JWMd/uun 3y JW,2 @r 4 ATTORNEYS.

Patented June 16, 1931 UNITED STATESE PATIENT OFFICE- EDWIN S. PRIDHAM, F OAKLAND, CALIFORNIA, ASSIGNOR TO THE MAGNAVOX COM- PANY, OF OAKLAND, CALIFORNIA, 'A CORPORATION OF ARIZONA SOUND I DIAPHRAGM Application filed Ma is,

My present invention relates to a sound diaphragm, such as are used commonly in con nection with sound reproducers.

' It is now well known that a diaphragm of comparatively large area can be actuated by a vibrating actuator, such as an electromagnetic reproducer or loud speaker unit. In

this way, the vibratory energy transmitted to the diaphragm by the unit is retransmitted by the diaphragm directly to theair to set or its equivalent isobviated.

One type of such a diaphragm takes the form of a thin element, such as parchment or paper, stretchedon a frame; and vibratory energy is imparted to the diaphragm adjacent its center. WVith such a device, it is found that only a limited amount of energy can be transmitted by the diaphragm to the up sound waves: and the necessityof ahorn airwithout serious distortion of the'sound;

and I believe this to be due to the fact that the diaphragm does not vibrate asa unit, but is most strongly actuated only adjacent its central point, the'remaining portions fie);- ing, under the stress of the mechanical vibrations. Thus when the actuating unitoperates strongly, the fiexure that results in the diaphragm probably causes the observed distortion.

It has been proposed to stiffen the diaphragm as by adding weight to it, in order to overcome this disadvantage. 'Yet such attempts are also unsatisfactory, because the inertia imparted to" the diaphragm causes other forms of distortion. In fact, observations lead to the generalization that the lighter and stiffer a diaphragm is made, the more faithful is its reproduction.

- It is, thus one of the objects of my inven- 4a tion to produce an extremely light diaphragm and to actuate it in such manner that the distortions discussed hereinbefore are largely avoided. I 1

In another form of diaphragm, use is made 1;; of a light stifi' cone, actuated at its small end. This is generally satisfactory, except that, more material being used, its inertia is larger than that of a flat diaphragm, and there is greater possibility of distortion due 5a. to the weight. The cone being stiff, it moves 1929. Serial No. 363,312. A

as a unit under actuation; and distortion due to flexure is prevented. It is another object of my invention to obtain the advantages of such a cone structure, while yet reducing the Weight of the diaphragm to a limit below that possible of attainment with a cone. 7 I

My invention contemplates the use of a substantially flat thin diaphragm; andI actuate the diaphragm not near the center, but remote therefrom. Thus there is greater assurance that the diaphragm will move as a unit when actuated.

'I find that best results can be obtained with the diaphragm "w-henactuated by a unitthat moves with a plunger-like action; for example, such as an electrodynamic unit having a coil attached to the diaphragm and axially movable under the influence of the signaling impulses. Due to the use of such a plungerlike motion, there is increased assurance that the whole diaphragm will movc'as a unit without undue fiexure.

My invention possesses many other advantages, and has other objects which may be made more easily apparent'from a consider ation of one embodiment of my invention.

For this purpose I have shown a form in the drawings accompanying and forming part of the present specification. I shall now proceed todescribe thls form in detail, which 7 illustrates the general principles of my invention; but it is to be understood that this detailed description is notlto'be taken in a limiting sense, since thescope of my invention is best defined by the appended claims;

Referring to the drawings i Figure 1 is a rear view of the diaphragm with the electromagnetic portions removed; and v Figure 2 is 'a side view of a diaphragm embodying myinvention, shown in connection with a dynamic unit, said unit as well as the supporting means for the diaphragm bcing iiidicated diagrammatically.

It is the main purpose of my-invention to eliminate weight asmuch as possible and yet-.pretain stifi'ness- IVith this end in view,

Iutilize a paper diaphragm 11,shown in desired manner.

novel features of my invention.

of legs or struts in an axial direction.

this instance circular; the size can of course vary, but I find that a diameter of about eight inches is satisfactory. The diaphragm can be supported at its edge in any Preferably I utilize a flexible annulus 12 fastened to the edge and clamped between stationary rings 13, l t. The annulus or band 12 can be made from thin leather or other readily pliant material, so that the diaphragm 11 while supported. has nevertheless considerable freedom of motion in a direction transverse to 1ts plane.

The diaphragm 11 is arranged to be actuated in a plunger-like manner. For this purpose, I show a movable coil 15 that is influenced bv signaling currents to move axially in an annular air gap 16 that is magnetized as by a field coil 17. Since the operation of dynamic units to etl ect such results is now well known, further elucidation thereof is considered ui'mecessary.

The manner in which the coil 15 1s connected to the diaphragm 11 is one of the A For this purpose I use a spider 18 made from thin stiii' paper, and formed at one end into a cylinder 19 on which coil 15 is supported. Radiating from the cylinder 19 are a number 20 (four being shown in this instance). These logs diverge at an angle from the cylinder and can be formed integrally therewith. The free ends of the legs 20 are made wider than the inner ends in order to ensure stiffness, and are fastened as by shellacking or pasting. to the back of diaphragm 11. I or facilitating this, each leg has a flange 21 that presents a Hat parallel surface adjacent the diaphragm and to en sure rigidity. I also provide a. ring 22 on the diaphragm, to which the legs can be directly fastened. This ring can be made also of paper of slightly greater thickness than the remainder of the diaphragm, and can be fas tuned to it, as by pasting.

I find that I can secure sufficient r1gid1t-y of structure even if the paper of the diaphragm 11 is only six one-thousandths of an inch thick; and the spider 18 can be made from even thinner paper. The reenforemg ring can be slightly thicker; say ten onethousandths of an inch. Of course these thicknesses can be materially departed from and yet the benefits of my invention may be obtained.

The manner of operation of my lnventlon can now be explained. When signaling currents are fed to coil 15, and the annular field 16 is energized, this coil 15 will vibrate The diaphragm 11 is actuated by these vibrations in a zone represented by ring 22, that is remote from its center. The diaphragm 11 thus moves as a unit, with little flexures due to the large area of the surface that is subJected to the vibrations, and to its remoteness from the axis.

When constr cted in the manner disclosed, I find that I can reduce the weight of the structure to a very low value; considerably less than that of an equivalent cone. Thus in one embodiment, the weight of the dia phragm 11 and coil 15 was about six grams. \Vith such little weight, the disturbing effects of inertia are also very much reduced.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. In an air actuating structure, a substantially flat, thin vibratory diaphragm, means for flexibly supporting said diaphragm near its edge, and means for transmitting vibrations to said diaphragm in a direction trans verse to its plane, and a reinforced surface disposed annularly around the center of the diaphragm upon which said. last means acts.

2. In an air actuating structure, a thin fiat diaphragm, and means attached to said diaphragm for transmitting vibrations thereto, including a light stiff spider structure having a cylindrical coil support at one end, and a number of diverging legs at the other end, said legs diverging outwardly and being fastened to the diaphragm.

3. In an air actuating structure, a thin flat diaphragm, and means attached to said diaphragm for transmitting vibrations thereto. including a light stiff spider structure having a cylindrical coil support at one end, a reenforcing annular ring attached to the diaphragm, and a plurality of diverging legs extending from the cylindrical support to the ring.

1. In an air actuating structure, a thin flat diaphragm, and means attached to said diaphragm for transmitting vibrations thereto, including a light stiff spider structure, and a reenforcing annular ring attached to the diaphragm, said spider structure having a plurality of diverging legs fastened to the ring.

5. An air actuator for loud. speakers comprising a fiat diaphragm having a limp flexible support at its outer edge, whereby it may move as a whole with a piston like movement, an annular reinforcing means secured to said diaphragm between its center and edge, an actuating means for driving said diaphragm, and a plurality of pyramidal disposed legs extending from said actuating means to said reinforcing means upon the diaphragm, whereby the actuating force will bG CllStTibuted over the surface of said diaphragm.

In testimony whereof I have hereunto set my hand.

EDWIN S. PRIDI'IAM. 

